The present invention relates to a covering device for ceramic modules having electronic components which are arranged between a ceramic substrate and an upper covering plate of the covering device.
A covering device of this type is needed for high-frequency ceramic modules, in order to shield the components on the surface of the ceramic substrate, fitted with components, and to protect them against mechanical damage. When the covering devices are put onto the ceramic substrates, subsequent mechanical deformations of the covering device are necessary in order to fix the covering devices to the ceramic module with a form fit. In the process, the ceramic substrates can be damaged. In particular in the case of highly complex multilayer HF ceramic modules, damage of this type entails high losses.
The object of the present invention is to provide a shielding device which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which can be fixed to the ceramic module without subsequent mechanical deformation.
With the above and other objects in view there is provided, in accordance with the invention, a covering device for a ceramic module of the type having electronic components arranged on a surface of a ceramic substrate, the covering device comprising:
an upper covering plate to be disposed above the electronic components on the surface of the ceramic substrate;
spacers supporting the covering device on the surface of the ceramic substrate fitted with the electronic components;
snap-in elements on at least two opposite side edge areas of the covering device, said snap-in elements engaging with at least one of a frictional fit and a form fit in lateral cutouts formed in the ceramic substrate and corresponding to said snap-in elements.
In other words, the covering device is supported on the surface of the ceramic substrate, fitted with components, via spacers, and the covering device has, on at least two opposite side edge areas, snap-in elements which engage with a frictional and form fit in lateral cutouts in the ceramic substrate corresponding to the snap-in elements.
The subject of the invention has the advantage that, with the snap-in elements, the different dimensions of the ceramic substrates, which are subject to high production fluctuations, can be compensated for, since the covering device adapts to the outlines of the ceramic substrate within wide limits during assembly. It is therefore not necessary for specific tolerance classes for the covering device to be kept in store, instead one covering device can be used for a wide range of tolerance classes of ceramic modules.
When the covering device is put onto a ceramic module, the snap-in elements are deliberately overstretched and then snap back again into the initial position as a result of their spring action, engaging in the cutouts in the ceramic substrate. At the same time, by means of a frictional fit in the plane parallel to the component fitting surface, the covering device is fixed and, by a form fit in the direction perpendicular thereto, the Z direction, the covering device is prevented from becoming detached from the ceramic substrate as it is put onto a printed circuit board or during subsequent further processing to form an end product. Because of the snap-in elements, mechanical reworking of the covering device is no longer required, so that the reject rate is reduced considerably, since damage both to the ceramic substrate and to the covering device is avoided. Furthermore, the handling and process sequence are significantly simplified.
In accordance with an added feature of the invention, the covering device is provided for box-shaped ceramic modules in HF technology and is itself of box-like design, the spacers used being angle pieces supported in the corner regions of the surface of the ceramic substrate fitted with components, while side edge areas of the box-like covering device are spaced apart from the surface fitted with components.
For the purpose of engaging with a form fit in the cutout in the ceramic substrate, at least one snap-in element has a form-fitting element for the fixing in the Z direction, the Z direction extending vertically with respect to the surface of the ceramic substrate fitted with components. The form-fitting element of a snap-in element substantially comprises an angled portion or a projection of the snap-in element in the direction of lateral cutouts in the ceramic substrate.
In addition to the form-fitting element, a snap-in element has at least one frictional-fitting part, which fixes the covering device in the X-Y plane, which extends parallel to the surface of the ceramic substrate fitted with components. A frictional-fitting part of this type in one embodiment comprises a snap-in element arranged on opposite sides, the frictional-fitting part itself comprising two springs which press the snap-in element onto the ceramic substrate. When four snap-in elements are provided, engaging with four sides of the ceramic substrate, such a frictional fit in the X-Y plane is implemented with further increased security.
In one embodiment, a snap-in element has a lug which is preshaped in an L-shape and whose longitudinal limb extends laterally along the ceramic substrate and whose transverse limb engages in the lateral cutout in the ceramic substrate. Such a lug-like design of the snap-in elements has the advantage that the snap-in elements and the covering plate of the covering device can be formed from the same material, specifically advantageously a sheet-metal strip. A sheet-metal strip of this type can be produced from spring bronze, from sheet iron, which shields electromagnetic waves, or from aluminum sheet. The L-shaped lug can already be designed as a leaf spring on its longitudinal limb.
In a further embodiment of the invention, the snap-in element is arranged with its upper end on the upper covering plate of the covering device. This arrangement makes it possible for snap-in elements arranged in pairs to be spread apart from each other with the aid of a spreading tool and to snap back into their initial form as soon as the lateral cutout on the ceramic module has been reached, wherein cutout the snap-in elements engage.
In a further embodiment of the invention, the snap-in element is arranged with its upper end in the center of a torsion beam, which is molded into the upper covering plate. In this embodiment, the snap-in element may be stiff in its longitudinal extent, since the torsion beam molded into the upper covering plate performs the spring action. In order to shape a torsion beam out of the upper covering plate, a U-shaped cutout is formed in the covering plate, its side limbs defining the length of the torsion beam and its transverse limb defining a first longitudinal side of the torsion beam. The snap-in element is arranged with its upper region on a second longitudinal side of the torsion beam, located opposite the first longitudinal side. When the snap-in element is spread with the aid of a spreading tool, at the same time the torsion beam molded into the covering plate is rotated and springs back into its initial position as soon as the formfitting element of the snap-in element has reached the cutout in the ceramic substrate, and therefore the snap-in element engages in the cutout after the spreading tool has been removed.
In a further embodiment of the invention, the ceramic substrate has transverse grooves in its edge areas. By using the transverse grooves, the individual layers of a multilayer ceramic substrate can be connected to one another by means of external metallization of the transverse grooves. However, the transverse grooves can also be used to solder dowel pins or contact pins to the ceramic module.
In a further embodiment of the invention, the ceramic substrate has a plurality of ceramic layers, conductor track layers and layers with thin-layer components such as resistors and capacitors, it being possible for the conductor tracks of the conductor track layers of the multilayer ceramic substrate to be connected electrically via plated-through contacts or via contacts in the transverse grooves. By means of such an embodiment of the high-frequency of the ceramic module, extremely complex circuits can be constructed in a very compact way, can be shielded by the covering device and protected mechanically.
In a further embodiment of the invention, the snap-in element can have a solder tab for soldering the covering device with ceramic substrate onto a printed circuit board. Such a solder tab combined with the snap-in elements at the same time achieves the situation where displacement of the ceramic substrate on the printed circuit board or loss of the covering device on the printed circuit board is ruled out.
In a further embodiment of the invention, side edge areas of the covering device are penetrated by openings and divided into a plurality of side edge sections. These side edge sections are for their part spaced apart from the surface of the ceramic substrate that carries components, while angle pieces in the corners of the ceramic substrate are supported on the corners of the ceramic substrate, determining the spacing as spacers. With the aid of dividing the side edge areas into a plurality of individual, separate side edge sections independent of one another, detrimental effects of different expansion coefficients of the ceramic substrate and of the covering device, such as thermal stresses, are avoided, particularly since the side edge sections are spaced apart from the ceramic substrate.
In a further preferred embodiment of the invention, a side edge section adjacent to the snap-in element has a projection which is supported on the surface of the ceramic substrate fitted with components. With this projection, the situation is advantageously achieved where an abutment is formed against the bending forces of the snap-in elements which otherwise act on the ceramic substrate. Without this projection of a side edge section, supported on the ceramic substrate as an abutment, a bending load would be exerted on the ceramic substrate with respect to the corner angles of the covering device by the snap-in elements, which are engaged approximately centrally with the ceramic substrate, in the cutouts. The bending load acts as a tensile stress, in particular in the upper ceramic layers, and could lead to microcracks in the ceramic substrate. In order to prevent this risk, the projection of the side edge section, which is adjacent to the snap-in element, forms an appropriate abutment by being supported on the surface of the ceramic substrate fitted with components.
The covering device is used for ceramic modules and protects the latter against damage and shields the surface fitted with components against interference fields.
With the above and other objects in view there is also provided, in accordance with the invention, a method of producing a covering device which has the following method steps:
providing a metal sheet;
stamping out a preform from the metal sheet with a structure which has the features of the covering device in the plane of the metal sheet; and
angling the side edge areas, the angle pieces and the snap-in elements into their three-dimensional form.
Using this method, a covering device is produced with simple means and the device can have the features of the different embodiments of the covering device according to the invention. The step of stamping out and angling to form a three-dimensional box-like covering device can be furnished by a stamping tool in a corresponding stamping press in a stamping and pressing operation, so that the last two steps of the above production method can be carried out in combination. A covering device produced simply in this way can be introduced into an automatic mounting device as bulk goods and can be fed via such an automatic mounting device to the ceramic substrates to be covered.
In a method of covering a ceramic module with a covering device, in further method steps, a ceramic substrate having a cutout on two opposite sides of the ceramic substrate in each case for anchoring the snap-in elements is provided and, finally, by placing the covering device onto the surface of the ceramic substrate fitted with components, whilst spreading the snap-in elements by means of a spreading tool and guiding the snap-in elements along the sides of the ceramic substrate until the snap-in elements latch into the cutouts in the ceramic substrate, the final assembly of a covering device with HF ceramic modules is performed.
Covering the ceramic modules is therefore possible without mechanical reworking. In particular, the embodiment of the snap-in connection achieves reliable retention of the covering device on the ceramic substrate by means of a frictional and form fit. With the aid of the torsion spring, which is molded into the upper covering plate, no over-expansion of the covering material occurs during the mounting, nor any plastic deformation of the covering material. Furthermore, with the covering device according to the invention, sorting of the ceramic substrates by tolerance classes is dispensed with, since the covering device can be adapted to all the tolerance classes of a ceramic material by means of the snap-in elements.
In a method of fitting a ceramic module with covering device to a printed circuit board, solder tabs of the covering device are fitted into prepared positions on a printed circuit board, and the solder tabs can be soldered to the printed circuit board in order to fix the covering device with the ceramic substrate onto the printed circuit board. This achieves a secure soldered connection on the printed circuit board by means of the corresponding solder tabs of the covering device.
In the case of HF ceramic modules which need shielding and mechanical protection, the covering device according to the invention can be used with success. The ceramic substrate in this case, as a carrier, is fitted with SMD housings or chips and wired appropriately. The covering device is then put on and secured against falling off. This securing must both have mechanical strength and be capable of being soldered to a printed circuit board. This requirement is also met by the covering device according to the invention.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a covering device for ceramic modules, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.